Curtailed renewables might make this economical in the short term, but also provides the same benefit for competitive storage technologies (e.g. LiFePO4 batteries). You'd have to compare the LCOE for each over the lifetime of the installation, and I don't think thermal would stack up well.
Thoughts about the iron flow batteries from ESS? They're using an iron flow chemistry that doesn't require exotic stuff. Looks like they've been testing for a while at a bunch of sites, and brought their first 'real' non-test customer online this fall.
On paper to a layman, they look perfect for at least some applications. Very cheap and easy to build the "stacks", almost completely nontoxic/safe, and relatively easy to scale (I think they don't scale indefinitely with liquid tank size...that the plate surface area also matters?)
> scale indefinitely with liquid tank size...that the plate surface area also matters?)
For flow batteries, the plate area controls the charge/discharge rate and the tank size controls the capacity. In theory you can scale the capacity as far as you can build tanks; I don't know whether there are practical considerations of "self-discharge" or electrolyte degradation.